These inventions relate generally to seals for turbines and have particular application to air turbine starters and to seals used in such starters.
An air turbine starter is a device used to start a turbine engine, such as an aircraft jet engine. The air turbine starter is mounted by the jet engine, much as a starter for an automobile is located by the automobile""s engine. In order to start the jet engine, the air turbine starter is activated. The applicant for the present invention, Honeywell International, Inc., has for years successfully designed, developed and manufactured air turbine starters.
Referring to the drawings, FIG. 2 shows a prior art turbine face seal used in air turbine starters. The face seal includes a rotor 2 mounted to shaft 24 adjacent a bearing 26. The rotor 2 has an axially facing flange 3. The face seal further includes a stator 4 mounted to turbine exhaust housing 27. Disposed between the rotor 2 and the stator 4 is a carbon seal ring 5 that engages the flange 3 to form a seal. In a typical air turbine starter such the ATS 100 shown in FIG. 1, the rotation of the turbine wheel 22 can generate under certain circumstances a low pressure or xe2x80x9cvacuumxe2x80x9d on the downstream side of the wheel which is also the airside of the turbine seal. This differential pressure may result in large oil leakage rates if the turbine seal has any flaws or coke build up in the contact zone. The coke build-up destroys the flatness of the sealing contact surfaces between the rotor and the seal carbon ring. In particular, the coke can separate the two surfaces resulting in a clearance therebetween. As a result, an air/oil mist may be pulled from the bearings through the seal and into the turbine exhaust air. If 100 to 300 cubic centimeters (cc) of oil is displaced to the turbine exhaust air without detection by the pilot or ground crew, loss of the air turbine starter by turbine bearing failure is possible. While this air turbine starter has acceptable reliability and generally functions as desired, the sensitivity of the starter design to turbine seal flaws can result in significant maintenance expenses and downtime for the starter.
The present inventions provide an improved turbine and an improved bearing seal for turbines, such as may be used with an air turbine starter or with other turbine applications. In one or more aspects of the present inventions, a more reliable turbine seal is provided which can be easily put in place and may provide longer in service time before routine maintenance. The turbine seal may also be easily retrofit on a number of turbine configurations, with a limited amount of added structure. The improved turbine seal may use existing turbine configurations to produce a pressure differential across an existing turbine seal to reduce the amount of oil or other fluid leakage that might otherwise occur around the existing seal. It may also reduce the pressure on the contacting surfaces of the bearing seal, reducing heat and coke build up, and in the process increase the lifespan of the seal.
In one form of one aspect of the present inventions, a turbine starter assembly having a turbine wheel includes a seal for sealing around a turbine shaft downstream from the turbine wheel. A fluid conduit extends from a higher pressure area to a downstream side of the turbine wheel and to a point at an upstream side of the seal so that fluid pressure at the upstream side of the seal is greater than the fluid pressure on the downstream side of the seal. The higher pressure area would be an area where a pressure exists that is sufficiently higher than the pressure at the downstream side of the seal that a positive pressure differential is created from the upstream side of the seal to the downstream side of the seal. For example, the higher pressure area could be an inlet side of the turbine wheel, such as the turbine inlet or the buffer region behind a turbine shield. Other areas may also be used.
In another form of one aspect of the present inventions, a turbine assembly having a turbine wheel includes a seal for sealing around a turbine shaft downstream from the turbine wheel. A fluid conduit extends from an upstream side of the turbine wheel to a downstream side of the turbine wheel and to a point at an upstream side of the seal so that fluid pressure at the upstream side of the seal is greater than the fluid pressure on the downstream side of the seal. Preferably, there is a positive pressure differential from the upstream to the downstream side of the seal so that fluid flow would tend to be from the upstream side of the seal to the downstream side of the seal. In one preferred aspect of the inventions, an oil seal is downstream from the turbine wheel at approximately atmospheric pressure and the conduit feeds higher pressure air to the upstream side of the seal.
In another form of another aspect of one of the present inventions, a turbine has a turbine wheel with an upstream side and a downstream side and a turbine shaft for supporting the turbine wheel for rotation. A bearing is positioned about the turbine shaft and a seal is placed adjacent the bearing. A conduit extends from the upstream turbine wheel side to a point on the side of the seal opposite the bearing for providing a positive pressure differential across the seal from the conduit toward the bearing. In one preferred embodiment, a bore is formed in the front of the turbine wheel and extends along a central axis of the turbine wheel. A second bore is formed to extend from the first bore to a point external to the turbine wheel and the turbine shaft on the downstream side of the turbine wheel. Higher pressure air can then be shunted to the seal.
In a further form of another aspect of one of the present inventions, a method is provided for creating a pressure differential across a seal. A first bore is formed in a turbine wheel and a second bore is formed in the turbine wheel intersecting the first bore wherein the first bore opens on an upstream side of the turbine wheel and the second bore opens on a downstream side of the turbine wheel. In one preferred embodiment, the turbine wheel is supported through a set of bearings about a turbine wheel shaft and the bearings are sealed by a first seal. A second seal is provided on a side of the second bore opposite the first seal to provide a space or cavity for maintaining a pressure in the cavity higher than a pressure on the opposite side of the first seal. This method can be used to produce an improved seal for a turbine assembly that reduces oil leakage from the seal adjacent the bearing.
The seal may be disposed between the turbine and the housing. The seal assembly comprises a face seal, a non-contacting seal axially spaced therefrom to define an air filled annular chamber therebetween and a flow passage having an exit fluidly communicating with said chamber and an inlet fluidly communicating with a source of air.
The air filled chamber acts as a buffer separating the differential pressure generated by pumping of the turbine from the face seal. Thus if the face seal develops a flaw (due to coke build up on the contact face or grain pull out from the carbon face) the seal leakage is low even if the sealing faces separate.
In a further aspect of another of the present inventions, a turbine wheel may be provided that has a flow channel, conduit or other flow configuration that extends from a front face or other upstream portion of the turbine wheel to a downstream portion of the turbine wheel, so that air or other suitable fluid can pass through the turbine wheel. With this turbine wheel, conventional air turbine starters, for example, can be rebuilt, and new air turbine starters can be built incorporating one or more aspects of the present inventions. Additionally, the turbine wheel incorporating the conduit described herein can be included as a kit. In a preferred embodiment, the kit includes the turbine wheel having a first channel formed in the first face of the turbine wheel and a second channel extending from the first channel to the outside surface of the turbine wheel, such as at the hub surface, between the turbine wheel and the turbine shaft. A kit may also include other components that may be considered necessary to properly install the turbine wheel for its intended purpose, and such additional components may include a seal assembly, fasteners, and the like.